Grey partridge releasing experiment

Key findings

After a year, the re-sighting rate of fostered chicks was at least three times higher than that of non-fostered chicks.

The proportion of birds released by fostering that subsequently bred successfully was twice as high as that of birds released using other methods.

Post-release settlement depends on supplies of holding crops.

One of the targets of the UK Biodiversity Action Plan for grey partridge is to "maintain and expand the current range". Accordingly, the purpose of this project in the UK is to find the best methods of re-establishing grey partridges through releasing in areas where they have disappeared, and where a suitable environment has been restored. A review of methods in 2004 suggested that the most promising techniques were fostering bantam-reared and artificially-reared young to wild pairs which failed to produce their own chicks (ie. barren pairs), and releasing full-grown family coveys in autumn and pairs in spring.

We are field-testing these four methods on 26 sites split between East Anglia and southern England in a two-year project. In each region we follow the fates and breeding success of radio-tagged and colour-ringed birds of individuals released using all four techniques at one site (ie. intensive study site). At a further 12 sites (ie. extensive study sites), only one releasing technique is applied per year and the outcome is monitored by standardised spring and autumn counts of colour-ringed birds.

At three of our six fostering sites in southern England, we failed to find suitable barren pairs for our chicks. We therefore had to release them as non-fostered birds. This provided us with survival data for birds released in a way similar to that traditionally used for shooting releases, already known to produce very low survival rates. Here, we present preliminary results from the first year of releases, 2004/05.

In March 2005, the re-sighting rate from the spring counts for fostered birds released in August 2004 across intensive and extensive sites averaged 11% in East Anglia and 21% in southern England. That of birds released as full-grown family coveys in November 2004 averaged 14% in East Anglia and 20% in southern England (see Table 1). No data were available for the spring pairs as they were released after these counts (in April). As in other studies, the majority of losses were due to predation.

Table 1: Re-sighting rate (%) of released grey partridge at all sites in East Anglia and southern England, based on the number of marked birds seen during the 2005 spring and autumn counts

In the following autumn, the average re-sighting rate of fostered birds was 16% in East Anglia and 9% in southern England. The releases of full-grown birds yielded re-sighting rates of 7% for autumn coveys and 21% for spring pairs in East Anglia and 7% and 12% respectively in southern England (see Table 1).

In terms of fidelity to the release site, the number of ringed individuals in spring 2005 within a radius of 1.5 kilometres of the release point seemed to depend largely on the availability of holding crops and varied between one and 25 individuals. The sites with winter rape or game crops including second-year kale were the ones where the highest number of pairs were recorded. Sites without suitable holding cover remaining in late February produced the lowest counts. At such sites, most released birds were found on neighbouring estates, in either rape, late stubbles, set-aside or game crops.

The percentage of all released females found with broods in autumn (all strategies combined) was nearly three times higher in East Anglia (34%) than in southern England (12%). Bantam-reared fostered females performed the best (48% of 27 females counted) followed by artificially-reared fostered females (42% of 19 counted). Spring-released females appeared to breed better (23% with broods, of 26 counted) than autumn-released females (only 5% with broods, of 21 counted).

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